ixgbevf: allow to set MTU

The support of jumbo frames in the ixgbevf Poll Mode Driver of 10GbE
82599 VF functions consists in the following enhancements:

- Implement the mtu_set function in the ixgbevf PMD, using the IXGBE_VF_SET_LPE
  request of the version 1.0 of the VF/PF mailbox API for this purpose.

- Add a detailed explanation on the VF/PF rx max frame len negotiation.

Signed-off-by: Ivan Boule <ivan.boule@6wind.com>
Signed-off-by: David Marchand <david.marchand@6wind.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

lib/librte_pmd_ixgbe/ixgbe_ethdev.c

@@ -220,6 +220,8 @@ static int ixgbe_remove_5tuple_filter(struct rte_eth_dev *dev,
 static int ixgbe_get_5tuple_filter(struct rte_eth_dev *dev, uint16_t index,
 			struct rte_5tuple_filter *filter, uint16_t *rx_queue);
 
+static int ixgbevf_dev_set_mtu(struct rte_eth_dev *dev, uint16_t mtu);
+
 /*
  * Define VF Stats MACRO for Non "cleared on read" register
  */
@@ -376,6 +378,7 @@ static struct eth_dev_ops ixgbevf_eth_dev_ops = {
 	.stats_reset          = ixgbevf_dev_stats_reset,
 	.dev_close            = ixgbevf_dev_close,
 	.dev_infos_get        = ixgbe_dev_info_get,
+	.mtu_set              = ixgbevf_dev_set_mtu,
 	.vlan_filter_set      = ixgbevf_vlan_filter_set,
 	.vlan_strip_queue_set = ixgbevf_vlan_strip_queue_set,
 	.vlan_offload_set     = ixgbevf_vlan_offload_set,
@@ -3937,6 +3940,40 @@ ixgbe_get_5tuple_filter(struct rte_eth_dev *dev, uint16_t index,
 	return -ENOENT;
 }
 
+static int
+ixgbevf_dev_set_mtu(struct rte_eth_dev *dev, uint16_t mtu)
+{
+	struct ixgbe_hw *hw;
+	uint32_t max_frame = mtu + ETHER_HDR_LEN + ETHER_CRC_LEN;
+
+	hw = IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
+
+	if ((mtu < ETHER_MIN_MTU) || (max_frame > ETHER_MAX_JUMBO_FRAME_LEN))
+		return -EINVAL;
+
+	/* refuse mtu that requires the support of scattered packets when this
+	 * feature has not been enabled before. */
+	if (!dev->data->scattered_rx &&
+	    (max_frame + 2 * IXGBE_VLAN_TAG_SIZE >
+	     dev->data->min_rx_buf_size - RTE_PKTMBUF_HEADROOM))
+		return -EINVAL;
+
+	/*
+	 * When supported by the underlying PF driver, use the IXGBE_VF_SET_MTU
+	 * request of the version 2.0 of the mailbox API.
+	 * For now, use the IXGBE_VF_SET_LPE request of the version 1.0
+	 * of the mailbox API.
+	 * This call to IXGBE_SET_LPE action won't work with ixgbe pf drivers
+	 * prior to 3.11.33 which contains the following change:
+	 * "ixgbe: Enable jumbo frames support w/ SR-IOV"
+	 */
+	ixgbevf_rlpml_set_vf(hw, max_frame);
+
+	/* update max frame size */
+	dev->data->dev_conf.rxmode.max_rx_pkt_len = max_frame;
+	return 0;
+}
+
 static struct rte_driver rte_ixgbe_driver = {
 	.type = PMD_PDEV,
 	.init = rte_ixgbe_pmd_init,

lib/librte_pmd_ixgbe/ixgbe_rxtx.c

@@ -3883,7 +3883,20 @@ ixgbevf_dev_rx_init(struct rte_eth_dev *dev)
 	PMD_INIT_FUNC_TRACE();
 	hw = IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
 
-	/* setup MTU */
+	/*
+	 * When the VF driver issues a IXGBE_VF_RESET request, the PF driver
+	 * disables the VF receipt of packets if the PF MTU is > 1500.
+	 * This is done to deal with 82599 limitations that imposes
+	 * the PF and all VFs to share the same MTU.
+	 * Then, the PF driver enables again the VF receipt of packet when
+	 * the VF driver issues a IXGBE_VF_SET_LPE request.
+	 * In the meantime, the VF device cannot be used, even if the VF driver
+	 * and the Guest VM network stack are ready to accept packets with a
+	 * size up to the PF MTU.
+	 * As a work-around to this PF behaviour, force the call to
+	 * ixgbevf_rlpml_set_vf even if jumbo frames are not used. This way,
+	 * VF packets received can work in all cases.
+	 */
 	ixgbevf_rlpml_set_vf(hw,
 		(uint16_t)dev->data->dev_conf.rxmode.max_rx_pkt_len);